Diecasting

Diecasting is the process of injecting molten metal under high pressure into cavities to create casts. A complete die casting cycle can range from less than one second (for parts weighing less than one ounce) to a few minutes (for parts weighing several pounds).

The earliest example of die casting dates back to the mid-1800s when a patent was awarded for the first manually-operated machine. In the early days of die casting, alloys consisted of a mixture of tin and lead, however, in 1914 zinc and aluminum were introduced and magnesium and copper followed shortly after. Today the more common alloys used in Canada include zinc, aluminum and magnesium.

There are two methods used in the die casting process: hot chamber and cold chamber. Hot chamber machines are typically used with alloys that have a low melting point, such as zinc and magnesium, while cold chamber machines are used for alloys with a high melting point such as aluminum.

In a hot chamber machine, an injection cylinder mechanism is immersed into the molten metal bath of a holding furnace, which is connected to the die via a “gooseneck,” or feed system. As the injection cylinder rises, a port opens and the molten metal flows into a holding chamber, filling it up. As the plunger lowers, the port is sealed, forcing the molten metal from the chamber through the gooseneck and into the die cavity. Once the metal has solidified the plunger is withdrawn, the die opens and the casting is ejected.

In a cold chamber machine the process is slightly different. Because of the properties of the alloys used, the molten metal is generally poured into the injection cylinder manually or automatically with a ladle. A hydraulically-operated plunger then seals the cold chamber port, forcing the molten metal into a locked die at a high pressure. This minimizes the amount of air entering the seal and prevents surface flaws in the finished product.

Dies generally have at least two sections, a fixed (cover) piece and a moving piece. Holes in the fixed piece, called sprues, allow for the molten metal to enter the die and fill the cavity while the moving piece has runners to route molten metal into the cavity. Dies also consist of locking pins to secure the two halves and ejector pins to allow for easy and quick removal of the completed cast. When a die is closed the two pieces are held together with hydraulic pressure or other locking devices.

The automotive sector accounts for more than 40 per cent of the die casting industry in North America. However, die casting is expansive and is used in many other sectors such as construction, agriculture, pulp and paper mills, medical, plumbing, railway and defence. Die casting creates toys, tools, household appliances and items for telecommunication.

There are two types of die casters: custom casters and captive casters. Custom die casters are those who create specialized casts for sale to others and captive die casters are those who create castings for their own use in a shop or manufacturing plant.

To assist Canadian die casters in dealing with government and other interested parties on industry-specific issues, the Canadian Die Casters Association (CDCA) was formed in 1976 and was incorporated in 1980. It gives the industry a united voice, which today remains effective and important.